Opaque plastic in Blender
Welcome to Blender Stack exchange. As wikipedia says 


  A polytunnel (also known as a polyhouse, hoop greenhouse or hoophouse, grow tunnel or high tunnel) is a tunnel typically made from steel and covered in polythene, usually semi-circular, square or elongated in shape.


I tried making a low-poly tunnel with least efforts quickly, it looks like this :


The way I achieved this is by


Modelling the polytunnel in the way I wanted.
Adding a transparent shader/glass shader as the material to make that plastic covering.


Here's the node setup for the material:


You can also use the glass shader, here's the usage: I can&#39;t make my material transparent in Blender 2.80